1. Field of the Invention
The present invention relates to machines, known as decorticating machines, for extracting usable fibre from the stems or leaves of certain plants, such as seed bearing plants, and in particular to the extraction of fibre from seed-flax once the linseed has been removed.
2. Discussion of Prior Art
It has long been known that the flax straw left after removal of seed contains fibres which, when separated from the associated pulp and woody matter, has a variety of uses. For example it can be used in the manufacture of paper, and it can be formed into a felt which might, for example, be used as a carpet backing or might be spun for woven cloth or a wick for soaking up oil. However, known methods of separating the fibre are either labour intensive or relatively inefficient, and as a consequence the flax straw is frequently treated as a waste product to be burned (which in many places is now not approved or is even illegal) or otherwise disposed of. Disposal other than by burning can be difficult as, due to its bulk and the long length it is difficult to chop and incorporate, and may take several years to break down under the action of soil organisms if it is ploughed back into the land.
In a known method of extracting fibres from flax straw the straw is first "retted" in large quantities of water, and is then beaten in a hand driven device to remove the unwanted material, which is known as shiv. This method produces a high quality fibre, but is extremely slow. Mechanised methods are known, as taught, for example, in U.S. Pat. No. 2,121,378 in which straw is passed in series through one or more pairs of crusher rollers, then through a series of decorticating rollers, the diameters of these decreasing in the direction of straw travel, to a pair of delivery rollers and thence through a rotating beater which acts over a grid through which waste material passes to a conveyance pipe, this last part of the process being pneumatically assisted. The various sets of rollers are fluted, and the process of separating fibre from shiv takes place as a result of the straw being, in effect, trapped between a series of interacting gears.
In another mechanical separating machine, described in EP 84302433.2 a similar process takes place in which the straw passes between sets of meshed gear wheels to separate the fibres from the shiv. With this apparatus the straw is to some extent aligned in the direction of travel by passing, prior to the crushing gears, over a grid through which pass spikes mounted on rotating wheels, the speed of rotation of the wheels increasing as the fibres near the crushing gears. A pinned roller (that is a roller from whose surface project a plurality of pins) combs out fibre from the material issuing from the crushing rollers, and this is collected whilst the shiv is led away for separate collection.
In practice these mechanised methods of extracting fibres have proved to have disadvantages, and the fibres produced thereby are held by some skilled in the art to be inferior to those produced by the old fashioned retting and hand operated separating process. There appear to be several reasons for this.
Whilst it appears that aligning the straw before it passes through crushing rollers has a beneficial effect it has been found that in arrangements such as that described in EP 84302433.2 straw tends to ride on top of the spikes rather than allowing the spikes to pass between them. It has also been found that using meshed gears to break down the bond between the fibres and the other material can lead to problems. Shiv breaking away from the fibres tends to clog the gears, and also to jam between adjacent sets of gear wheels so affecting the efficiency of the apparatus or even bringing it to a stop. Also the passage of the straw through the gear wheels has the effect of weakening the fibres so allowing them to become droopy with the result that they tend to droop down into the spaces between adjacent sets of gears, again with a loss of good usable fibres and with the danger of jamming the machinery. Furthermore these known apparatus do not make any provision for adjustment of the quality of the final fibre product to make allowance, for example, for different standards of straw input or For different output requirements such as a requirement for there to be a certain proportion of shiv left with the fibre. When fibre and shiv are delivered directly in the required proportion the distribution thereof is much more even than when an attempt is made to remix fibre and shiv after separation.